Modified globoid gearing



Allg. 16, 1966 P, 5 ZAK MODIFIED GLOBOID GEARING Filed May 14, 1964 FIG. Z FIG. 4

n 3,266,334 Ice Patented August 16 1966 3,266,334 MODIFIED GLOBOID GEARING Pavel Samoilovich Zak, Moscow, USSR., assignor to Vsesoyuzny Nauchno-lssledovatelsky i Proelitno-Telrhnologichesky Institute Ugoljnogo Mashinostrojenija, Moscow, U.S.S.R.

Filed May 14, 1964, Ser. No. 367,369 4 Claims. (Cl. 74-4S8) The present invention relates to enveloping worm gearings and more particularly, to enveloping worm gearings with a modified helix line of the operating and generating worms.

More specifi-cally, the present invention relates to enveloping 'worm Igearing comprising an hour-glass or throated worm and a worm gear with a concave root line in an axial section. Such worm gearing is sometimes called double-enveloping.

A conventional enveloping w-o-rm gearing is already known which is characterized by a constant angular lead of the worm thread equal t-o 211:1', wherein z =Z2:Z1 which is the gear ratio. The worm 4gear has teeth conjugate with such a worrn. This kind of gearing is also known as the Cone or Hindley type.

It has been already proposed t-o modify this conventional yform lof enveloping worm gearing by providing a ce-rtain divergence of the worm thread path from the thread `path of the conventional worm gearing. The 'worm thread pat-l1 of the enveloping worm is here defined as the curve obtained when the working surface of the worm thread is intersected by the surface of a torus coaxial with the worm. T-he circumference, by the rotation of which said torus is obtained, having its center offset from the axis of the worm by a value equal to the interaxial distance of the gearing, the surface of said torus being -disposed approximately midway between the surface of the top and the surface of the root of the worm threads.

Said modification of the enveloping worm is characterize-d by the value of divergence of its thread helix from `that of the conventional worm.

The best practical results have been obtained when Athe thread path -diverges into the body of the wcrlm thread at its ends. Lf the worm gear is conjugate to such worm, then the gearing differs liront the conventional one and is usually Icalled a modified enveloping worm gearing. The physical change Iof such divergence along the length of the worm starting `from its entering end is usually called the modification law and characterized by a modification curve Iwith the value of divergence or modification being plotted along the ordinate, and the value orf the angle of turn of the worm thread axial profile generatrix, along the ab-scissa starting from the entering edge thereof.

It has been also proposed and is technologically expedient to choose the modification ourve of the tform of a continuous smooth curve without cu-rve reversal, the best results in the service of gearings being obtained \when the extremum point of t-he modification curve, i.e., the point of minimum deviation of the modification curve lies `between the mid-portion o-f the worm and the exit end thereof.

The disadvantage of known solutions is the presence of an undercutting zone on the surface of .the worm gear toot-h which results in respective discontinuity of the field of contact. The underoutting is due to the penetration of: the exit portion of the worm thread which is beyond the minimum point of the modification curve, into the enveloping surface of the worm gear tooth. Stated otherwise, when the end of the worm thread passes the extremum or point of minimum deviation, it penetrates into and undercuts the subsequent enveloping surface.

Though attempts were made to eliminate this undercutting they proved to be of no commercial success. IIt is possible, of course, to establish a form of modification curve in 'whieh there Iwould 'be no undercutting on said exit portion of the worm thread. `It is much more important, however, to pro-vide the required form of the modification curve on the entering portion from the entering end of the worm thread up to the extremum point. It is rather diicult to satisfy both these conditions.

Therefore, I do not claim as my invention such gearing in which a definite -form of the modification curve on the exit portion of the worm is preset, or such gearing in which the form of the modlcation curve is modified on the entering portion of the worm, but I do claim s-uch gearing in which the entire exit portion of the worm beyond the extremurn point of the modification curve is brought out of mesh and the worm gear has teeth whose working surface is conjugate to said worm.

The applicant has established `that the form of t-he modification curve of the worm, including the magnitude of modification on the entering portion and lthe position of the extremum point is orf paramount importance for improving the service characteristics (wear resistance and efficiency) of the enveloping worm gearing. From a standpoint of a practical realization of such law orf modiiication, when manufacturing the working worm and the generating wor-m (hob) -great technological advantages may lbe gained with a modiiication curve close to a parabola or to any other similar curve without curve reversal.V

The applicant has also established that if, when choosing the modification curve, its form is predetermined as being most advantageous for t-he entering portion, then t-he exit portion is usually the source of the above-described undercutting, which also brings about deterioration of t-he contact conditions on the entering portion of the contact field due to .the fact that a portion of the tooth surface will be brought out of mesh.

The main object of the present invention is to provide such modified enveloping worm gearing in which there will be eliminated the undercutting of the enveloping surface of the worm gear tooth.,

Sai-d object is achieved by the use of a modified enveloping 'wor-m gearing which comprises an enveloping worm with a continuous modification curve of its thread helix directed into the thread body, and a worm gear whose teeth envelop the worm and are generated by a bob with the generating surface coinciding with the surface of the worm threads, in which enveloping worm gearing, in accordance with the invention, the surface of the worm threads is defined by the portion from the entering end to the extremum point of the modification curve; the teeth of the worm gear may also be generated by means of a hob with the generating surtt-ace coinciding with the surface of the worm threads in the mid-portion thereof and with a gradual divergence towards both its edges and along its height, the initial contact between the teeth of the worm gear and the threads of the worm being in the form of a zone localized in the mid-portion of the working surface of the worm thread with respect to the length and height of said thread and in the mid-portion of the working surface of the worm gear tooth so that in the azeaasa process of running-in, sai-d zone gradually and uniformly expands over the entire working surfaces o-f the worm threads and the worm gear teeth.

It is an object of the present invention to eliminate undercutting of the enveloping sunface of the worm gear tooth whereby a contact field is obtained constituted by two leaves with advantageous contact conditions on each of said leaves.

The present invention also eliminates the influence of unavoidable deformations as well as inaccuracies, arising in the process of .manufacturing and assembly, upon the operation of the worm gearing, which is ensured by the initial mating of the generating worm and the working worm in the midportion of the eld of contact.

The objects and advantages of the invention will become apparent from the Ifollowing description and accompanying drawings in which:

FIG. 1 diagrammatically represents the generation of the worm thread helix of an enveloping worm gearing;

FIG. 2 shows a field of Contact consisting of two parts and inherent to the conventional -form of the enveloping worm gearing;

FIG. 3 shows a modification curve of the worm thread helix in case of the entire length of the worm rbeing used; shown above is the initial surface of the worin torus;

FIG. 4 shows the field of Contact .corresponding to the modification of the curve of the :Worm thread which is shown in FIG. 3;

FIG. 5 shows Ithe modification curves of the working and generating worms; y

FIG. 6 shows the field of `contact correspon-ding to the enveloping worrn gearing lwith a wonm with no exit portion beyond the extremum point of the modification curve.

T-he lconventional form of the enveloping gearing is characterized by a constant ratio of the angular rota-tion speed w1 orf worm 1 and the angular rotation speed o2 of the profile generatrix (FIG. 1). Thereby, there will 'be generated a helical curve for the enveloping gearing on the worm 1. Stated in another way, the enveloping gearing defines an intersection with the worm constituted of a helical line extending along the worm =1.

rIhe field of conta-ct B of the modified enveloping worm gearing, corresponding lto the modification l-aw, the curve 2 or which is shown in F'IG. 3, has a diagonal form and a discontinuity due to undercutting as shown in FIG. 4. Modification curve 3 of the working worm and modification curve 4 of the generatrix worm (FIG. 5) are limited by the extremurn point A. The field of contact corresponding to the enveloping yworm gearing with a worm without the exit portion beyond the extremum point is divided i-nto two leaves as shown in FIG. 6, on each of said leaves .there -being advantageous contact conditions, the same as on portion A of the field of contact of the conventional enveloping worlm gearing shown in FIG. 2 and on the field of contact of a modified enveloping worm gearing with the use of the entire length of the wor-m (FIG. 4).

Another embodiment of the sarne concept is also possible, this time not by the elimination of the exit portion of the worm beyond the extremum point of a preset modification curve, but by changing the modification curve in such a way that the extremum .point of the modification curve tbe offset to the very end of t-he exit portion of the worm threads. Hence, in this case the Wonm threads will also have the working surface defined by the portion from the entering end to the extremum point of the .modification curve.

Modification curve 3 of the working worm and modiffication curve 4 of the generating worm (FIG. 5) coincide in one point 0 located in the mid-portion of the field of the field of contact, and diverge towards the ends thereof. Such a relative form of the modification curves provides for the initial mating of the gener-ating worm and the working worm in the mid-portion and, hence, excludes the zg. infiuence of unavoidable inaccuracies in the process of manufacturing and assembly.

In accordance therewith the initial contact between the worm and the worm gear will have t-he form of a certain point localized in the mid-portion olf the surface of the worm threads along the length and height thereo-f, as well as in the mid-portion of the working surface of the worm gear teeth.

As a limit the initial contact may be in the for-m of a point such as point 0' as shown in FIG. 5.

The clearances between the surfaces of the worm threads and the surfaces of the worm gear teeth should gradually increase from the initial point of contact towards the edges of the :working surfaces of the Iworru threads and the worm gear teeth, present-ing certain iianks which may be made either on the worm or on the worm gear. It is preferable to provide flanks on the worrn threads, though it is not essential and the flanks may be provided 4on the worm gear by changing the forrn of the generating fworm.

`In the course of runningin, the zone of contact expands from the mid-portion towards the ends finally enveloping the entire field of contact.

Though the present invention is described in accordance with the preferred embodiment thereof, various modifications of the described invention may be effected by persons skilled in the art without departing from the principle and scope of the invention as defined in the appended claims.

What is claimed is:

1. An enveloping worm gearing lcomprising a worm having opposite ends constituting `an entering end and an exit end, said .worm including a thread wound thereon aiong a continuous curved line .which deviates from a nonmail helical line, said curved line being tangential with said helical line at an inter-mediate point of extremus and deviating from said line from said extremus point towards the entering end of the worm, and a worm gear having teeth enveloping said worm and including working surfaces conjugate with said Worm.

2. An enveloping worm gearing comprising a worm having opposite ends constituting an entering and an exit end, said wor-rn including a thread wound thereon along a Icontinuous curved Iline which deviates from a normal helical line from the entering end to a point of minimum deviation, and a worm gear having teeth er1- veloping said wonm and including working surfaces conjugate with said worm, the thread of said worm having a sunface defined by the portion of the thread extending from the entering end to the point of minimum deviation.

3. An enveloping worm gearing comprising a worm having opposite ends constituting an entering end and an exit end, said worm including a thread wound thereon along a continuous curved line which deviates from a nor- =ma'l helical line, said curved line having an extremus point of minimum deviation from the helical line, said thread having a surface defined :by the portion of the curved line deviating from said helical line from the entering end to the vicinity of said extremus point such that said worm gearing is adapted to cooperate `with a worm gear having teeth with working 4surfaces conjugate to sai-d wor-rn thread and consequent initial contact at a prescribe-d contact point located centrally along the length of the thread surface and midway of the height thereof.

4. A modified enveloping worm gearing comprising an enveloping worm with a continuous modification curve of the helix of the thread thereof and free of curve reversal, and a worm gear Iwhose teeth envelop said worm; the initial contact of the wonm and the worm gear being limited by an ini-tial contact spot localized in the mid-portion of the field of contact along the length of said worm, the rest of the field of contact being provided with small clearances gradually increasing in the direction from the initial contact spot towards the ends of .the field of contact both along the height of the profile and along the vlength of said 5 6 Worm yso that during the initial Wear olf the worm gearing References Cited bythe Examiner in the 'course of its service there will be provided a grad- UNITED STATES PATENTS ual and uniform expansion of said Contact spot over the l I 1 entire Working surfaces `of the Worm threads and worm 3045557 N196@ Yamamoto et al' 'n 7 58 X gear teeth; the threads of said .worm having the sur-face 5 D AVID j. WILLIAMOWSKY primary Examineh ydefined by the portion between the entering end and up to a pre-established poi-nt in the vicinity of .the minimum DON A WAITE Exammer point `of deviation of the modication eurve. R. I. BIR'D, L. H. GERI'N, Assistant Examiners. 

1. AN ENVELOPING WORM GEARING COMPRISING A WORM HAVING OPPOSITE ENDS CONSTITUTING AN ENTERING END AND AN EXIT END, SAID WORM INCLUDING A THREAD WOUND THEREON ALONG A CONTINUOUS CURVED LINE WHICH DEVIATES FROM A NORMAL HELICAL LINE, SAID CURVED LINE BEING TANGENTIAL WITH SAID HELICAL LINE AT AN INTERMEDIATE POINT OF EXTREMUS AND DEVIATING FROM SAID LINE FROM SAID EXTREMUS POINT TOWARDS THE ENTERING END OF THE WORM, AND A WORM GEAR HAVING TEETH ENVELOPING SAID WORM AND INCLUDING WORKING SURFACES CONJUGATE WITH SAID WORM. 